The title of the project has been renamed. Last year's title was Characterization of NCp7 and Viral Peptides Bound to MHC Class I of HIV-1 Virions. Recent studies have indicated strong cellular immunity against HIV-1 epitopes. We have characterized allele-specific motifs of five human MHC Class I molecules which will allow a systematic search for HIV-1 epitopes that may be recognized by cytotoxic T lymphocytes restricted by HLA molecules. Tandem mass spectrometry was used to characterize the structural motif shared by peptides presented by Class I molecules HLA-A1, A2.1, A3, A11 and A24. Each HLA-A molecule binds peptides restricted in length to 8-10 amino acids and shows peptide motifs that are allele-specific with up to three anchor positions. All the naturally-processed peptides sequenced were synthesized and shown to bind well to the appropriate alleles. Naturally-processed peptides bound to MHC Class I molecules of HIV-1 infected B cells were also characterized. Two approaches were employed. The first method used to search for viral peptides was based on the retention time of known synthetic peptides that bound HLA-A2.1. No corresponding peptides were found with the correct mass and charge state. As an alternative to the synthetic approach, a subtractive method was used. Three peptides present in samples isolated from HIV-1 infected B cells which were not present in samples taken from normal cells were sequenced by tandem mass spectrometry. The peptides were each derived from vinculin which was shown to be over expressed as a result of HIV-1 infection. A cellular cytotoxic response was analyzed in patients with HIV-1 infection or healthy donors. Vinculin peptides induced in vivo and in vitro CTL priming; this finding may prove valuable in the search for an effective vaccine against HIV-1 virus.